Resolving the ‘opal paradox’ in the Southern Ocean

Philippe Pondaven (), Olivier Ragueneau, Paul Tréguer, Anne Hauvespre, Laurent Dezileau and Jean Louis Reyss
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Philippe Pondaven: Université de Bretagne Occidentale UMR CNRS 6539, Institut Universitaire Européen de la Mer
Olivier Ragueneau: Université de Bretagne Occidentale UMR CNRS 6539, Institut Universitaire Européen de la Mer
Paul Tréguer: Université de Bretagne Occidentale UMR CNRS 6539, Institut Universitaire Européen de la Mer
Anne Hauvespre: Université de Bretagne Occidentale UMR CNRS 6539, Institut Universitaire Européen de la Mer
Laurent Dezileau: Laboratoire des Sciences du Climat et de l’Environnement, Laboratoire mixte CNRS/CEA
Jean Louis Reyss: Laboratoire des Sciences du Climat et de l’Environnement, Laboratoire mixte CNRS/CEA

Nature, 2000, vol. 405, issue 6783, 168-172

Abstract: Abstract In the Southern Ocean, high accumulation rates of opal—which forms by precipitation from silica-bearing solutions—have been found in the sediment in spite of low production rates of biogenic silica and carbon in the overlying surface waters. This so-called ‘opal paradox’ is generally attributed to a higher efficiency of opal preservation in the Southern Ocean than elsewhere1,2. Here we report biogenic silica production rates, opal rain rates in the water column and opal sediment burial rates for the Indian Ocean sector of the Southern Ocean, which show that the assumed opal paradox is a result of underestimated opal production rates and overestimated opal accumulation rates. Our data thus demonstrate that the overall preservation efficiency of biogenic opal in this region is substantially lower than previously thought2, and that it lies within a factor of two of the global mean3. The comparison of our revised opal preservation efficiencies for the Southern Ocean with existing values from the equatorial Pacific Ocean and the North Atlantic Ocean shows that spatial differences in preservation efficiencies are not the primary reason for the differences in sedimentary opal accumulation. The reconciliation of surface production rates and sedimentary accumulation rates may enable the use of biogenic opal in the reconstruction of palaeoproductivity when the factors that affect the Si/C ratio are better understood.

Date: 2000
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DOI: 10.1038/35012046

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